Supply circuit for operation of an electromagnetic load

ABSTRACT

A supply circuit is provided for operation of an electromagnetic load of a vehicle provided with generator (dynamo) and battery, and more particularly for operation of at least one solenoid valve of a fuel-injection system of an internal-combustion engine of the vehicle. A circuit arrangement is proposed which connects the load (6) for a buildup of its excitation to the generator (3) and then establishes a connection to the battery (13) for the maintenance of sufficient excitation and interrupts the connection to the generator (3).

FIELD OF THE INVENTION

The present invention relates to a supply circuit for operation of anelectromagnetic load of a vehicle provided with a generator (dynamo) andbattery, and more particularly, for operation of at least one solenoidvalve of a fuel-injection system of an internal-combustion engine of thevehicle.

BACKGROUND OF THE INVENTION

When an electromagnetic load is switched on, the load current does notincrease suddenly; rather, it rises relatively slowly. As a result, theload comes up to its rating only with a certain time delay after theturn-on time. This peculiarity is a drawback in many technical devices.

In the case of electromagnetic injection valves of aninternal-combustion engine of a vehicle, this turn-on time delay isresponsible for the fact that the fuel injection time cannot bedetermined with sufficient accuracy. To overcome this drawback, it isknown to generate the control pulse for the solenoid valve in such a waythat a relatively high current surge (pull-in current) is present whichleads to very rapid actuation of the solenoid valve, and which isfollowed by a lower, steady-state current value (hold current) formaintaining the solenoid valve in its operated position. Electroniccircuits of great complexity are required for the generation of suchcontrol pulses. (German published patent application 28 28 678.)

SUMMARY OF THE INVENTION

The supply circuit of the present invention offers the advantage ofproviding, through relatively simple means for building up theexcitation of the electromagnetic load, in other words, for the pull-inphase of the solenoid valve, a sufficiently large current for thesolenoid valve to be actuated reliably and within a minimum of time.Once this state has been attained, a changeover to a considerably lowerenergy input occurs, that is, the load current is reduced to the holdcurrent of the solenoid valve. For the implementation of the operationjust described, the invention utilizes means already in place in thevehicle. These are the generator (dynamo) and the battery.

Since the generator charges the battery while the internal-combustionengine is in operation, its terminal voltage is made larger than that ofthe battery. The invention takes advantage of this by providing acircuit arrangement which connects the load (i.e., the solenoid valve)for a buildup of its excitation, in other words, for the pull-in phase,to the generator, so that it is supplied with a relatively high voltageresulting in rapid excitation. If in the exemplary embodiment hereconsidered the solenoid valve is the load, then it is actuated within avery short time. Once this state has been attained, that is, when theload is in its desired state of excitation, the circuit arrangementeffects, in accordance with the invention, such a changeover that aconnection to the battery is established to maintain sufficientexcitation and the connection to the generator is interrupted. Theexcitation is preferably reduced to a value which, though relativelylow, is sufficient to maintain the valve in its operated position. Thepull-in current flowing initially can consequently be reduced to thehold current.

As a further feature, the invention provides for a voltage booster to belocated between generator and load. This makes it possible to send in arelatively short time a very large current through the excitation coilof the solenoid valve. With an inductance of 170 millihenrys, forexample, the pull-in current pulse is preferably of the order ofmagnitude of 70 amperes. A voltage of the order of about 100 volts isthus required. The voltage booster consequently must raise the vehicleelectrical system voltage, which usually is between 12 and 14 volts, tothat voltage level.

In a preferred embodiment of the invention, the voltage booster isdesigned as a transformer. The generator is preferably analternating-current generator; a three-phase generator, in particular,may be used.

A rectifier may be connected between generator and load. This rectifiermay be located in particular between the transformer which forms thevoltage booster and the solenoid valve. In the case of a three-phasegenerator, the three-phase alternating voltage produced is thus firsttransformed and then rectified. The three-phase arrangement has theadvantage that the rectified direct voltage has a relatively low ripple.

To be able to provide sufficient energy for the pull-in phase of thesolenoid valve, an energy-storage device may be used. The latter may beconnected, in particular, following the rectifier and may be in the formof a capacitor.

The changeover from the described pull-in operating mode to the holdmode is performed by means of controllable switching devices of thecircuit arrangement. Preferably, one switching device is connected tothe generator, and another to the battery. These two switching devicespass the load current to the load by way of diodes connected in theforward direction. These diodes decouple the two energy sources(generator or energy-storage device and battery) from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an electrical system of a motor vehicle;

FIG. 2 is a block diagram of a generator and a voltage booster;

FIG. 3 shows a circuit arrangement which is connected to the system ofFIG. 2 and supplies a plurality of solenoid valves of a fuel injectionsystem of an internal-combustion engine of the vehicle;

FIG. 4 (a) to (c) shows the circuit arrangement of FIG. 3 in variousswitching states;

FIG. 5 is a diagram of a rectified generator voltage; and

FIG. 6 is a current-time diagram of a solenoid valve.

DETAILED DESCRIPTION

FIG. 1 shows an internal-combustion engine 1 of a vehicle (not shown).The internal-combustion engine 1 is connected through a V-beltarrangement 2 with a generator (dynamo) 3 designed as a three-phasegenerator. The internal-combustion engine 1 has four cylinders.Consequently, four injection valves 4 are provided. These are designedas solenoid valves 5 and therefore represent electromagnetic loads 6.

The solenoid valves are connected through lines 7 to a controller 8which cooperates with a computer 9. The latter has inputs 10 to whichthe information necessary for determination of injection time, injectionquantity and injection duration is routed.

The controller 8 is connected through a line 11 to the generator 3 andthrough a line 12 to a battery 13 of the vehicle. There is, moreover, aconnection 14 between the generator 3 and the battery 13. The connection14 assures the recharging of the battery 13.

FIG. 2 shows diagrammatically in detail the makeup of the generator 3.The latter comprises a rotor 15 and a stator 16 as well as a controller17 of the electronic type, which is indicated in the drawing by thesymbol for a transistor. The stator 16 is connected through lines 18 toa voltage booster 19 in the form of a transformer 20. While the primarywinding P of the transformer 20 is connected to the stator 16 of thegenerator 3, its secondary winding S is connected to a rectifier 21. Therectified transformer voltage is available at terminals 22 and 23.

The terminals 22 and 23 of FIG. 2 are connected to correspondingterminals 22' and 23' of FIG. 3. Terminal 22' is grounded at 24, thatis, connected to the chassis of the vehicle. The negative pole of thebattery 13 is also grounded at 24. The positive pole of the battery 13is connected to a terminal 25. Consequently, the battery voltageU_(Batt) is present between terminal 25 and ground 24, and the generatorvoltage U_(Gen), stepped up by the transformer 20 and rectified by therectifier 21, between terminal 23 or 23', respectively, and ground 24.

The terminals 22', 23' and 25 are part of a circuit arrangement 26 whichcomprises controllable switching devices S1, S2, S3, S4, S5 and S6. Theswitching devices S1 to S6 can be placed in their ON or OFF state bymeans of a control device (not shown in detail) of the circuitarrangement 26 or by means of the controller 8.

While one terminal 27 of the switching device S1 is connected toterminal 25, its other terminal 28 is connected to the anode of a diodeD1. The cathode of diode D1 is connected to a tie point 29.

Inserted between the terminals 22' and 23' is a capacitor C which formsan energy-storage device 30. Terminal 23' is further connected to oneterminal 31 of the switching device S2. The other terminal, 32, ofswitching device S2 is connected to the anode of a diode D2 whosecathode is connected to the tie point 29. Through lines 33, whichinclude line 7 of FIG. 1, the tie point 29 is connected to one lead ofeach excitation coil 34 of the solenoid valves 5. The other leads of theexcitation coils 34 are connected to terminals 35, 36, 37 and 38 of theswitching devices S3, S4, S5 and S6. The other terminals 39, 40, 41 and42 of the switching devices S3, S4, S5 and S6 are connected to a busline 43 which, through a precision resistor 44, is connected to groundat 24. Connected in parallel with the precision resistor 44 is a currentregulator 45 which cooperates with devices of the controller 8 toprovide for an optimal current supply to the solenoid valves 5.

The supply circuit in accordance with the invention, shown in FIGS. 2and 3, for the solenoid valves 5 operates as follows:

Suppose that the controller 8 seeks to perform an injection of fuel intothe first cylinder Zyl1 of the internal-combustion engine 1 (FIG. 4a).The first cylinder Zyl1 is assigned to switching device S3 while thesecond cylinder Zyl2 cooperates with switching device S4, the thirdcylinder Zyl3 with switching device S5, and the fourth cylinder Zyl4with switching device S6. For the operation of the first cylinder Zyl1,the controller 8 drives the switching devices S2 and S3 into theirclosed states so that a pull-in current I_(A), driven by the generatorvoltage U_(Gen), flows through the excitation coil 34 of solenoid valve5, assigned to the first cylinder Zyl1. As a result of the voltage boostby the transformer 20, the generator voltage U_(Gen) may have arelatively high value. Besides, in addition to the direct energizationby the generator 3 there is the energy stored in the capacitor C.Overall, a strong and rapidly rising pulse of pull-in current I_(A) isthus generated, as is apparent from FIG. 6. The time t₁ there signifiesthe switching on of the excitation coil of solenoid valve 5 of cylinderZyl1. At time t₂ (FIG. 6), switching device S2 of the circuitarrangement 26 is reset into its open position (FIG. 4b), and switchingdevice S1 is simultaneously set to its closed position. As a result, theexcitation coil 34 of solenoid valve 5 of the first cylinder Zyl1 isdisconnected from the generator voltage U_(Gen) and at the same timeconnected to the battery voltage U_(Batt). Since the battery voltageU_(Batt) is smaller than the generator voltage U_(Gen), as mentionedearlier, the current flowing through the excitation coil 34 drops,decreasing to a hold current I_(H) that is sufficient for maintainingthe solenoid valve in its operated position. The drop in the current isclearly apparent from FIG. 6: From time t₂, the current through theexcitation coil decreases to the hold current I_(H).

At time t₃ (FIG. 6), the switching devices S1 and S3 (see FIG. 4c) open,with the current then dropping to a value of 0.

The energization of the other excitation coils 34 of the solenoid valves5 associated with the cylinders Zyl2, Zyl3 and Zyl4 is effected in thesame manner.

It is apparent from the foregoing that the buildup of the excitation ofthe excitation coil 34 of the appropriate solenoid valve 5 is broughtabout directly by the energy supplied by the generator 3, "directly"allowing for the use of a voltage booster and of a rectifier. For themaintenance of sufficient excitation to hold the solenoid valve 5 in itsoperated position, the energy supplied by the battery 13 is used.

FIG. 5 shows that the voltage supplied by the three-phase generator,stepped up by the transformer 20 and rectified by the rectifier 21, hasa relatively low ripple, as pointed out earlier.

We claim:
 1. A supply circuit for operation of an electromagnetic loadof a vehicle having a generator and battery, and a load including atleast one solenoid valve of a fuel-injection system of aninternal-combustion engine of the vehicle, comprising:a circuitarrangement which connects the load to the generator for a buildup ofexcitation of the load, and then establishes a connection of the load tothe battery and interrupts the connection of the load to the generatorfor the maintenance of sufficient excitation of the load.
 2. A supplycircuit as defined in claim 1, further comprising the voltage boostercoupled between the generator and load.
 3. A supply circuit as definedin claim 2, wherein the voltage booster includes a transformer.
 4. Asupply circuit as defined in claim 1, wherein the generator is analternating-current generator.
 5. A supply circuit as defined in claim1, wherein the generator is a three-phase generator.
 6. A supply circuitas defined in claim 1, further comprising a rectifier connected betweenthe generator and load.
 7. A supply circuit as defined in claim 1,further comprising an energy-storage device coupled to the rectifier. 8.A supply circuit as defined in claim 7, wherein the energy-storagedevice includes a capacitor.
 9. A supply circuit as defined in claim 1,further comprising two controllable switching devices, one of theswitching devices being connected to the generator, the other switchingdevice being connected to the battery, and both switching devices beingconnected to the load through corresponding diodes for controllingcurrent flow to the load.
 10. A supply circuit for operating a pluralityof injection valves of a fuel-injection system of an internal-combustionengine, comprising:a generator selectively coupled to the injectionvalve for positioning the injection valves in an operating state; and abattery selectively coupled to the injection valves for maintaining theinjection valves in the operating state.
 11. A supply circuit as recitedin claim 10, further comprising a transformer, wherein the input of thetransformer is coupled to the generator, and the output of thetransformer is coupled to the injection valves.
 12. A supply circuit asrecited in claim 11, further comprising a rectifier coupled to theoutput of the transformer.
 13. A supply circuit as recited in claim 12,further comprising an energy-storage device coupled between the outputof the rectifier and ground.
 14. A supply circuit as recited in claim13, wherein the energy-storage device includes a capacitor.
 15. A supplycircuit as recited in claim 13, further comprising two controllableswitching devices for selectively coupling the generator and battery,respectively, to the injection valves.
 16. A supply circuit as recitedin claim 15, further comprising a current regulator and a resistorcoupled in parallel and selectively coupled to the injection valves. 17.A supply circuit as recited in claim 16, wherein the generator is analternating-current generator.
 18. A supply circuit as recited in claim16, wherein the generator is a three-phase generator.